1. Field of the Invention
The present invention relates to embedding data in material. Embodiments of the present invention relate to watermarking.
Material as used herein means information material represented by information signals and material includes at least one or more of image material, audio material and data material. Image material is generic to still and moving images and includes video and other forms of information signals represents images.
2. Description of the Prior Art
Steganography is the embedding of data into material such as video material, audio material and data material in such a way that the data is imperceptible in the material.
Data may be embedded as a watermark in material such as video material, audio material and data material. A watermark may be imperceptible or perceptible in the material.
A watermark may be used for various purposes. It is known to use watermarks for the purpose of protecting the material against, or trace, infringement of the intellectual property rights of the owner(s) of the material. For example a watermark may identify the owner of the material.
Watermarks may be “robust” in that they are difficult to remove from the material. Robust watermarks are useful to trace the provenance of material which is processed in some way either in an attempt to remove the mark or to effect legitimate processing such as video editing or compression for storage and/or transmission. Watermarks may be “fragile” in that they are easily damaged by processing which is useful to detect attempts to remove the mark or process the material.
Visible watermarks are useful to allow e.g. a customer to view an image e.g. over the Internet to determine whether they wish to buy it but without allowing the customer access to the unmarked image they would buy. The watermark degrades the image and the mark is preferably not removable by the customer. Visible watermarks are also used to determine the provenance of the material into which they are embedded.
FIG. 1 shows one such known apparatus, generally 100, for embedding a transform domain watermark in an image. The image 105 is received by the transformer 110 and output as a transform domain image 115. The transform domain watermark 145 is then applied to the transform domain image 115 by the combiner 120 which outputs a transform domain watermarked image 125. The transform domain watermarked image 125 is then received by the inverse transformer 130 and output as a spatial domain watermarked image 135.
However, a problem arises in that the image 105 may be degraded by the operation of both the transformer 110 and inverse transformer 130. The transformers 110, 130 need to be very accurate to ensure that any degradation is minimised. Accurate transformers are relatively expensive and two are required.